Five Britons have been arrested in connection with a suspected plot to use explosives to disrupt the G20 summit.

The individuals, who are political activists unaffiliated to any terrorist organisation, were arrested at addresses in Plymouth. They are being held under terrorism legislation.

Despite the involvement of explosives, a police source with knowledge of the investigation has told the Guardian that initial inquiries indicate the five were "not planning a Guy Fawkes plot".

"I think it was more designed to disrupt than injure or kill," the source said, adding that reports that the individuals were Greek nationals were false.It is understood that the quantity and type of material found at the addresses indicates a small-scale stunt.

Scotland Yard has issued a series of warnings in recent days that protesters are planning to bring the capital to a standstill this week in potentially violent protests scheduled to coincide with the arrival of world leaders for the summit, in east London.